Why complicate things when you can replace your cameras with three regular camcorders and be free? The Canon XA series are great, and so is the Sony EA50; even the 'somewhere on the ocean' Blackmagic Pocket Camera if you can't afford the bigger cameras.
If your shooting long interviews, a camera that doesn't run the possiblity of overheating (almost every new 4k) that doesn't break a long taping into multiple clips (almost every high def tapeless camera) probably would not be an option.
I'd look at either buying a used 2k eng**** (if you have enough light) or renting a large eng. I would even look at tape, because with all it's issues, people still use tape (many more than you'd think) and collecting tape is not the hardest thing in the world, or the most expensive.
As goofy and single purpose that eng cameras look and function, for long news type interviews they have a purpose.**
Chris S can weigh in on this as he has a lot of interviews style experience.
I know I just shot an interview in NY (not for reproduction, to just build a style board) in NY Tuesday with the gh3's. It worked fine, ran for 1 and 1/2 hours, change cards then another 45 minutes.
The only issue is the gh3 breaks the take into about 6 cuts which have to be assembled. Also long takes start adding noise.
Had I used a tape camera like the XA canons*, I could have run for hours, plugged it into something simple like I-movie or fcp 7 and collected it in one clip, one take.
The deeper us still photo guys get into video and motion imagery, we start to learn that some of the old ways were around for a reason and worked very well.
* I would write a semi large check if Canon came out with a modern version of a tapeless xl1 with a super 35mm cmos single chip. If you ever used the sd xl1 camera (the sd version not the 3 ccd high def version) you would realize how really good a video camera can be. It looked like film, it ran for hours, it had non hobbled settings, xlr inputs, big batteries, great, great, great sound mixer and a lot of lenses, both auto servor and manual. The sound was so good, that a big time foley house in Hollywood, still uses them with a lens cap on just to record foley sound.
Canon stopped that form factor for some reason, (probably because of dslrs and the planned c series) but for most of us going from still to motion, a high def xl1 with a big chip, would have been the deal.
** Sony is the leader in video looking video. They make jewel like cameras, actually wonderful machines and the only issues I've ever had with them is they look just like tv news coverage video.
If that's what I was after, I'd have bought Sony straight away, but I've tested all of them, many, many times and they had only two issues. They looked like video, not film, they loved interlace at 30 ot 60 I and for the tape versions, Sony's never really liked any deck but Sony, which was about 10 times the price of everyone else.
*** As still photographers moving to motion, we're kind in a no mans land. Not really long form film makers, not really video guys that shoot with blue jell backgrounds. We want our imagery to look like moving film, we want 2 to 4k, we want to use lens styles, viewfinders and form factors we understand (hence dslrs).
I personally think certain cameras are very good for certain genres and styles and I know that tomorrow if I found a 2k eng. and it would go to 800, 1000 iso clean I'd buy it as long as it had a deep pretty file.
Honestly, if I was doing more interviews I'd look at the tapelsss versions of the X, the XA http://www.bhphotovideo.com/c/product/733533-REG/Canon_4888B001_XF100_HD_Professional_Camcorder.html
They shoot a clean pretty file except at high iso (high db), shoot 50mbs (which is bbc standards), the lenses are sharp and good, the autofocus is good and doesn't hunt and they costs less than a recorder for a dslr. You kind of have to use one to see how good it is.
The only issue is to get a sturdy Pelican case and don't bump them around too much because parts break easy and be careful of all the tiny little buttons, because accidentally pushing the wrong button can make your life hell.
In fact with a lot of light, my Canon X's were very good, shot a beautiful file, never had an issue with tape, and I loved using them when dof and light wasn't an issue. The only problem was the XA's were not that sturdy, compared to the Xl1's. Those damn xl1's just never stopped working and never broke, (almost), where the X's even in a strong pelican case couldn't be moved across the street without the onboard mic or the secondary mic holder breaking.
When I used them, sometimes I would hire a real news videographer that usually used Sony. After seeing the footage, they all bought the Canon X (like 4 different guys) because the files looked so good and the cameras are cheap (in motion camera terms).
Sorry for the long response, but I've been there, done that, spent a lot of money of cameras that set on shelves and I know that what is really needed (ask Chris S) is a video camera form factor camera that shoots a film like file.Actually here's what I want.
An adjustable 4k to 2k camera that goes from 24p (real p not faux p), manual and autofocus, minimum 50mbs, preferably 72 to 100mbs, a video camera form factor, xlr inputs, native pro rezz 422 file, 12 bit, long takes without fan noise, without overheating, additional viewfinder that really is sturdy and looks like a viewfinder not a small plastic tv., Canon xl batteries, clean +12 db, shoots to large cf cards without issue (with two slots for backup).
Real full size xlrs, hdmi, connectors that are sturdy and at least 3 built in ND filters.
$4,000 tops for the body, really about $2,500 . . . and not another 10 grand for a module, or a to come 4k file, or all the other to come stuff that digital comes with.
Actually what I want is a panasonic gh3 in a video cam form factor, higher iso and well, that'll do it.